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The impossibility of one body's receiving another within itself, or the impossibility of two bodies' occupying the same space at the same time. Impenetrability is not resistance, which seems to be an active quality; nor is penetration to be identified with absorption or similar phenomena, which are the result of the porous or reticular structure of matter. The fact of impenetrability is a datum of sensible experience.

The search for a causal explanation of impenetrability arises from the theological consideration of the glorified body of Christ, and from speculation about the glorified bodies of the blessed. Christ's emergence from the sealed tomb at the Resurrection and His entrance through the closed doors of the Upper Room represent suppressions of the natural impenetrability of bodies (see resurrection of christ). Discussion of such miracles leads to an analysis of the nature and cause of impenetrability.

Two opposing solutions were offered in the Middle Ages. St. thomas aquinas sees impenetrability as an effect, in the order of formal causality, of the accident of quantity. Bodies are numerically diverse by reason of their dimensions, dimensions follow on situation (situs ), and situation derives from quantity (In Boeth. de Trin. 4.3; In 4 sent. In the terminology of later commentators, impenetrability is a secondary formal effect of the accident of quantity, something negative and arising from the relationship of a body to place. John Duns Scotus holds that impenetrability is an active force, the result, in the order of efficient causality, of quantity (In 4 sent. 49.16).

Most 20th-century scholastics follow the solution of St. Thomas. Others, while not accepting Scotus's reasons, agree with him in assigning a positive, active nature to impenetrability. All concur that God can miraculously suppress impenetrability as an effect, while retaining intact the quantity that is its cause.

See Also: location (ubi); bilocation; extension.

Bibliography: j. gredt, Elementa Philosophiae AristotelicoThomisticae, ed. e. zenzen, 2 v. (13th ed., rev. and augm. Freiburg 1961) 1:279282. p. hoenen, Cosmologia (5th ed. Rome 1956). a. tognolo, Enciclopedia filosofica, 4 v. (VeniceRome 1957) 2:129394.

[w. b. mahoney]

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